1. Field of the Invention
The present invention relates to a display device, and more particularly, to a liquid crystal display device and a method of fabricating the same. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for effectively controlling liquid crystal flow in fabricating a liquid crystal display.
2. Discussion of the Related Art
In general, applications of liquid crystal display devices have characteristics, such as full color realization, low voltage operation, low power consumption, thinness, lightness in weight, and high image quality. Thus, its applications have been diversified from monitors for electronic watches, calculators, notebook computers, personal computers and TV's, and monitors for aviation gauges, personal digital assistants (PDA's), and mobile stations.
A method of forming a liquid crystal layer is largely classified into two methods, such as a liquid crystal injection method and a liquid crystal dispensing method. As a panel of the liquid crystal display device becomes larger in size, the liquid crystal dispensing method is mostly used in fabricating the liquid crystal display device. This is because the liquid crystal injection method takes more time to inject the liquid crystal between first and second substrates. In the liquid crystal dispensing method, liquid crystal droplets are dispensed on one of the first and second substrates, and then the substrates are bonded to each other to form the liquid crystal layer.
When the liquid crystal is injected between the first and second substrates, a thermo-hardening sealant is usually used. For instance, epoxy resin is mixed with amine or amide in order to form a thermo-hardening sealant. The thermo-hardening sealant is hardened by applying heat to the sealant for about one or two hours at a temperature of about 100°, so that contamination of the liquid crystal may occur due to a long hardening time period. In the liquid crystal dispensing method, the first and second substrates are attached to each other with a photo-hardening sealant. In this case, the photo-hardening sealant is a mixture of a hardener and acryl resin. When UV-ray is irradiated to the sealant, the hardener becomes a radical, and then the radical acts with the acryl resin, so that the acryl resin is activated. Accordingly, the mixture is polymerized so that adhesion of the sealant is improved. After forming the liquid crystal layer between the first and second substrates, the UV-ray is irradiated to the attached substrates in order to harden the sealant between the first and second substrates for several seconds. In addition, a ball spacer is used between the first and second substrates so as to maintain a cell gap in the liquid crystal injection method. Meanwhile, a column spacer is used between the first and second substrates so as to maintain a cell gap in the liquid crystal dispensing method.
A related art liquid crystal display device and a method of fabricating the same will be explained with reference to the accompanying drawings.
FIG. 1 is a plane view of a liquid crystal display device according to a related art liquid crystal dispensing method. FIGS. 2A to 2G are plane views illustrating process steps of fabricating a liquid crystal display device according to a related art liquid crystal dispensing method.
In FIG. 1, a plurality of gate lines 80 and a plurality of data lines 90 are formed to cross one another in an active region 120 of a thin film transistor array substrate (i.e., a first substrate) 100, thereby defining a plurality of pixel regions. A pixel electrode 112 is formed at each pixel region. A plurality of thin film transistors (not shown) are formed at each corresponding crossing point of the gate and data lines 80 and 90 so as to apply signals of the data lines to each pixel electrode 112 according to signals of the gate lines. Then, the liquid crystal (not shown) is dispensed on the first substrate 100.
Next, a color filter array substrate (i.e., a second substrate) 150 includes column spacers, a black matrix layer 130, and a photo-hardening sealant. In this case, the column spacers 105 are formed on the second substrate 150 so as to maintain a cell gap between the first and second substrates 100 and 150. The black matrix layer 130 is formed in the periphery of the active region 120. The photo-hardening sealant 110 surrounding the black matrix layer 130 is formed in the periphery of the black matrix layer 130 so as to attach the first and second substrates 100 and 150 to each other. After attaching the first and second substrates 100 and 150 to each other with the photo-hardening sealant 110, UV-ray is irradiated to the attached substrates from the top of the second substrate 150 for hardening the photo-hardening sealant 110, thereby bonding the first and second substrates to each other.
At this time, there may occur imperfect or excessive filling of the liquid crystal if the exact amount of the liquid crystal is not dispensed on the substrates. When the amount of the liquid crystal dispensed on the substrate is less than the required amount, it takes time to spread the liquid crystal from the center of the substrate to the corner regions, such as the farthest spots. As a result, a tilt angle of the liquid crystal may be changed since a contaminant is accumulated on the liquid crystal display panel. On the other hand, when too much liquid crystal is dispensed on the substrate, spots may appear on the liquid crystal display panel due to a problem in the spacer for maintaining a cell gap between the first and second substrates.
A method of fabricating a liquid crystal display device according to a related art liquid crystal dispensing method will be explained in detail.
FIGS. 2A to 2G are plane views illustrating fabricating process steps of a liquid crystal display device according to a related art liquid crystal dispensing method. In the liquid crystal display device according to the related art liquid crystal dispensing method, a plurality of liquid crystal display panel regions are formed on first and second substrates. A thin film transistor array and a color filter array are respectively formed on the first and second substrates. Then, a liquid crystal is dispensed on the substrate, and a sealant is deposited thereon. After attaching the substrates to each other, each substrate is cut into unit liquid crystal display panel regions, thereby forming the liquid crystal display panel regions on each substrate.
More specifically, in FIG. 2A, a plurality of gate lines (not shown) are formed on the first substrate 100, and a plurality of data lines (not shown) are formed on the first substrate 100 to cross one another, thereby defining a plurality of pixel regions. A pixel electrode (not shown) is formed at each pixel region, and the thin film transistors (not shown) are formed at each crossing point of the gate and data lines for applying signals of the data lines to each pixel electrode according to signals of the gate lines. Also, a common line (not shown) is formed for applying a voltage to a common electrode. In this case, a plurality of liquid crystal display panel regions 99 are formed on the first substrate 100. Then, a plurality of silver (Ag) dots 101 are formed on the common line of each liquid crystal display panel region 99 to provide an electrical connection to the common line. The liquid crystal 103 is appropriately dispensed on each liquid crystal display panel region 99 of the first substrate 100.
As shown in FIG. 2B, a black matrix layer (not shown), a color filter layer (not shown), and a common electrode (not shown) are formed on the second substrate 150. A column spacer 105 is formed on each liquid crystal display panel region 99 of the second substrate 150 corresponding to the gate and data lines of the first substrate 100. Then, a photo-hardening sealant 110 is formed in the periphery of each liquid crystal display panel region 99 of the second substrate 150, as shown in FIG. 2C.
In FIG. 2D, the first substrate 100 is placed under the second substrate 150. The first and second substrates 100 and 150 are loaded to a bonding apparatus with a controllable vacuum chamber. The surface of the second substrate 150, on which the sealant 110 is deposited, faces down, and then is fixed to an upper stage 170 that moves along the Z-axis direction (i.e., vertical direction). Also, the first substrate 100 is fixed to a lower stage 160 that moves along the XY-axis direction (i.e., horizontal direction). After that, the second substrate 150 fixed to the upper stage 170 and the first substrate fixed to the lower stage 160 are aligned, and the chamber of the bonding apparatus is in a vacuum condition, thereby attaching the first and second substrates 100 and 150 to each other, as shown in FIG. 2E. Then, the first and second substrates are attached to each other with a first gap.
Subsequently, as shown in FIG. 2F, gas or dry air is provided to the chamber of the bonding apparatus under a vacuum condition so as to equalize the pressure of the chamber with the atmospheric pressure. Accordingly, the first and second substrates attached by the sealant 110 are maintained under vacuum, and the circumferential area of the substrates is under the atmospheric pressure, so that the first and second substrates are pressed to each other due to a pressure difference between the inside pressure of the substrates and the atmospheric pressure. Simultaneously, the liquid crystal 103 spreads out on the entire liquid crystal display panel between the first and second substrates, thereby forming a liquid crystal layer 103a. Then, the UV-ray is irradiated to the attached substrates from the top of the second substrate 150, thereby hardening the photo-hardening sealant 110.
However, the related art liquid crystal display device according to the liquid crystal dispensing method and the method of fabricating the same have the following disadvantages.
When the dispensed amount of the liquid crystal is too much on the substrate, a uniform cell gap cannot be maintained between the first and second substrates since a buffer region, in which the liquid crystal may move around, cannot be formed in the liquid crystal display device when the substrates are attached to each other. On the other hand, when the dispensed amount of the liquid crystal is not enough on the substrate, it is difficult to regulate the liquid crystal flow in the related art liquid crystal display device since the buffer region cannot be formed therein.